Re: [PATCH v2 2/2] mm/pageblock: remove false sharing in pageblock_flags

[Alex Shi]

在 2020/8/19 下午3:57, Anshuman Khandual 写道:
> 
> 
> On 08/19/2020 11:17 AM, Alex Shi wrote:
>> Current pageblock_flags is only 4 bits, so it has to share a char size
>> in cmpxchg when get set, the false sharing cause perf drop.
>>
>> If we incrase the bits up to 8, false sharing would gone in cmpxchg. and
>> the only cost is half char per pageblock, which is half char per 128MB
>> on x86, 4 chars in 1 GB.
> 
> Agreed that increase in memory utilization is negligible here but does
> this really improve performance ?
> 

It's no doubt in theory. and it would had a bad impact according to 
commit e380bebe4771548  mm, compaction: keep migration source private to a single 

but I do have some problem in running thpscale/mmtest. I'd like to see if anyone
could give a try.

BTW, I naturally hate the false sharing even it's in theory. Anyone who doesn't? :)

Thanks
Alex